Field
This disclosure related to digital active filters for use in a listener's ear to modify ambient sound to suit the listening preferences of the listener.
Description of the Related Art
Humans' perception to sound varied with both frequency and sound pressure level (SPL). For example, humans do not preceive lower and higher frequency sounds as well as they perceive sounds at midrange frequencies between 500 Hz and 6,000 Hz. Further, human hearing is more responsive to sound at high frequencies compared to low frequencies.
There are many situations where a listener may desire attenuation of ambient sound at certain frequencies, while allowing ambient sound at other frequencies to reach their ears. For example, at a concert, concert goers might want to enjoy the music, but also be protected from high levels of mid-range sound frequencies that cause damage to a person's hearing. On an airplane, passengers might wish to block out the roar of the engine, but not conversion. At a sports event, fans might desire to hear the action of the game, but receive protection from the roar of the crowd. At a construction site, a worker may need to hear nearby sounds and voices for safety and to enable the construction to continue, but may wish to protect his or her ears from sudden, loud noises of crashes or large moving equipment. Further, a user may wish to engage in conversation and other activities without being interrupted or impaired by annoyance noises such as sounds of engines or motors, crying babies, and sirens. These are just a few common examples where people wish to hear some, but not all, of the sounds in their environment.
In addition to receiving protection from unpleasant or dangerously loud sound levels, listeners may wish to augment the ambient sound by amplification of certain frequencies, combining ambient sound with a secondary audio feed, equalization (modifying ambient sound by adjusting the relative loudness of various frequencies), noise reduction, addition of white or pink noise to mask annoyances, echo cancellation, and addition of echo or reverberation. For example, at a concert, audience members may wish to attenuate certain frequencies of the music, but amplify other frequencies (e.g., the bass). People listening to music at home may wish to have a more “concert-like” experience by adding reverberation to the ambient sound. At a sports event, fans may wish to attenuate ambient crowd noise, but also receive an audio feed of a sportscaster reporting on the event. Similarly, people at a mall may wish to attenuate the ambient noise, yet receive an audio feed of advertisements targeted to their location. These are just a few examples of peoples' listening preferences.
Throughout this description, elements appearing in figures are assigned three-digit reference designators. An element not described in conjunction with a figure has the same characteristics and function as a previously-described element having the same reference designator.